1. Field of the Invention
The present invention concerns a cleaning article using a water-decomposable non-woven fabric which is dispersed easily by a water stream and, more in particular, it relates to a cleaning article of low density and having high surface strength.
2. Related Art
Cleaning articles formed with water-decomposable non-woven fabrics are used for the cleaning operation of wiping human skins such as on hips or for cleaning toilets and thereabouts. The cleaning articles can be directly flushed away in toilets after use.
Japanese Patent Laid-Open No. 229295/1990 discloses a water-decomposable non-woven fabric used for cleaning articles of this kind in which a non-woven fabric formed of water dispersible fibers contains carboxymethyl cellulose (CMC) as a water soluble binder and also contains a polyvalent metal salt for preventing dissolution of the water soluble binder in a wet state thereby improving the wet strength.
Further, Japanese Patent Laid-Open No. 228214/1997 discloses a product prepared by entangling under a water stream regenerated cellulose fibers having a fiber length of 4 mm to 20 mm and pulp fibers by a water jetting treatment, which intends to establish a balance between the strength and the water decomposability of the non-woven fabric by selecting the fiber length of the regenerated cellulose fibers.
In Japanese Patent Laid-Open No. 229295/1990 the water soluble binder is impregnated into the entire non-woven fabric formed of the water dispersible fibers to improve the strength of the non-woven fabric in the wet state. However, in the fabrics of this type, since the water soluble binder is impregnated into the non-woven fabric generally by using a spray, while the tensile strength of the entire non-woven fabric can be increased to some extent, the strength at the surface of the non-woven fabric can not be improved sufficiently.
Accordingly, fluffing often occurs on the surface of the non-woven fabric during wiping of dirt, or the surface of the non-woven fabric is often broken upon wiping of firmly deposited dirt.
Further, when the surface strength is intended to be improved by increasing the strength for the entire non-woven fabric, the amount of the binder to be impregnated into the non-woven fabric has to be increased. However, when the water soluble binder is impregnated by spraying into the non-woven fabric, there is a limit for the amount of the binder that can be impregnated into the non-woven fabric. Further, for impregnating a great amount of the water soluble binder into the non-woven fabric and improving the wet strength, it is necessary to incorporate a great amount of a metal salt in a wet state to bring about a problem in view of safety to human skins.
Then, in Japanese Patent Laid-Open No. 228214/1997, it is intended to improve the strength and make the water decomposability favorable by selecting the fiber length of the regenerated cellulose fibers. However, it is actually difficult to appropriately make a balance between the strength and the water decomposability. Moreover, since the entire strength is intended to be obtained merely by the entangled state of the fibers, the surface strength of the non-woven fabric is extremely low and the non-woven fabric involves a problem that the fibers appearing on the surface drop off during wiping operation or the surface of the non-woven fabric is broken easily.
The present invention intends to overcome the foregoing problems in the prior art and it is an object thereof to provide a cleaning article by using a non-woven fabric of satisfactory water decomposability, in which the surface strength of the non-woven fabric is increased thereby enabling to prevent fluffing on the surface and dropping of fibers upon wiping operation and, further, prevent breakage on the surface, as well as a manufacturing method thereof
In accordance with the present invention, the foregoing object can be attained by a cleaning article comprising a water-decomposable non-woven fabric containing water dispersible fibers and a water soluble resin coated on at least one side of the water-decomposable non-woven fabric, in which the water soluble resin is contained more in a surface portion of a fiber assembly than in a remaining portion of the fiber assembly.
Here, when the water soluble resin is coated on both sides of the non-woven fabric, the remaining portion of the fiber assembly, as sandwiched between two surface portions, may be called xe2x80x9cinner portionxe2x80x9d or xe2x80x9cintermediate portionxe2x80x9d. For convenience in illustrating the invention, therefore, the term xe2x80x9cinner portionxe2x80x9d is used hereinafter for describing the remaining portion, it being understood that the term xe2x80x9cinner portionxe2x80x9d never intends to limit the invention to the case where the water soluble resin is coated on both sides of the non-woven fabric.
The cleaning article of the invention can be produced, for example, by coating the water soluble resin on one side or both sides of the water-decomposable non-woven fabric in the state of a solution with a viscosity ranging from 1,000 cps to 100,000 cps.
In this case, the solution of the water soluble resin (for example, which is prepared by dissolving the water soluble resin in water or purified water) has such a high viscosity that it adheres mainly to the surface portion (surface layer), on one side or on each side of the non-woven fabric, without being impregnated uniformly into the non-woven fabric. Accordingly, in a state where the fiber web of the water decomposable non-woven fabric is dried, the amount of the water soluble resin adhered (or deposited) to the fibers is greater in the surface portion (surface layer) of the non-woven fabric than in the inner portion thereof.
Preferred range of the viscosity is from 5,000 cps to 70,000 cps and, further preferably, from 10,000 cps to 70,000 cps.
When the viscosity of the solution of the water soluble resin is less than 1,000 cps, the solution is impregnated almost uniformly into the non-woven fabric so that the water soluble resin can not be deposited sufficiently on the fibers of the surface layer. But, too much addition of the water soluble resin is undesirable. In this case, therefore, it is difficult to improve the surface strength of the non-woven fabric to a desired degree. When the viscosity is from 1,000 to less than 5,000 or 10,000 cps, the uniform impregnation of the solution can be prevented but it is still relatively difficult to permit only the surface layer to have a sufficient strength.
On the other hand, if the viscosity exceeds 100,000 cps, it is difficult to coat the solution uniformly on the surface of the non-woven fabric due to such a high viscosity. When it is 70,000 cps or less, the solution can be coated uniformly with no problem.
As described above, when the solution of the water soluble resin at a high viscosity is coated on the surface of the water-decomposable non-woven fabric and the amount of the water soluble resin in the surface layer is more than that in the inner portion, only the surface strength of the cleaning article can be improved satisfactorily. This enables prevention of fluffing on the surface, dropping of fibers and breakage at the surface upon wiping, and it also enables readily wiping of firmly deposited dirt.
The fiber density of the water-decomposable non-woven fabric is preferably 0.3 g/cm3 or less.
In such a relatively bulky non-woven fabric having a low fiber density, a water soluble resin easily intrudes between fibers. Therefore, if a solution of a water soluble resin at a low viscosity is added by use of a spray as in the prior art, the water soluble resin comes into the inner portion of the non-woven fabric, so that it is difficult to improve only the surface strength of the non-woven fabric. In the invention, on the other hand, because the solution of the water soluble resin at a relatively high viscosity is coated on the surface, on one side or each side of the non-woven fabric, the water soluble resin can be maintained in the surface layer of the non-woven fabric to a desired degree. As a result, according to the invention, even in such a bulky non-woven fabric having a low fiber density, the surface strength can be improved. That is, the invention is suitable for a cleaning article comprising such a relatively bulky non-woven fabric having a low fiber density.
The average fiber length of fibers constituting the water-decomposable non-woven fabric is preferably 10 mm or less and, more preferably, 7 mm or less.
By the use of the fibers having such a short fiber length for the non-woven fabric, when the cleaning article is flushed in a flushing toilet, the fibers are easily dispersible, thereby improving the water decomposability of the cleaning article. In addition, since the surface strength of the non-woven fabric is improved by the water soluble resin, these short fibers is prevented from dropping off from the surface of the non-woven fabric.
The amount of coating of the water soluble resin is preferably from 0.5 g to 30 g based on 100 g of the fibers forming the water-decomposable non-woven fabric. Here, the coating amount of the water soluble resin is measured after drying the solution. If the coating amount is less than the lower limit described above, the surface strength of the non-woven fabric can not be improved sufficiently. On the other hand, when the coating amount exceeds the upper limit, the softness of the non-woven fabric is decreased.
The cleaning article of the invention preferably has such a softness in a dry state that the B value (which indicates the bending rigidity) of the cleaning article in a dry state as measured according to a KES bending test is from 0.05 or more to 1.0 or less. In the invention, used is the bulky non-woven fabric of a low density and therefore, the rigidity is not excessive and the softness is excellent. In addition, even for such bulky non-woven fabric of a low density, because the solution of the water soluble resin at a high viscosity is coated on the surface of the non-woven fabric thereby forming the water soluble resin-containing surface layer, the rigidity (B value) of 0.05 or more as described above can be attained.
When the cleaning article of the invention is prepared for use in a wet (moistened) state, an insolubilizing agent for the water soluble resin is preferably added. This can maintain the wet (moistened) strength of the cleaning article at a high level. However, the cleaning article of the invention may be used in a dry state as it is.
In such a wet state, the cleaning article of the invention preferably has such a softness that the B value (which indicates the bending rigidity) of the cleaning article in a wet state as measured according to a KES bending test is 0.03 or more. In this case, the upper limit is preferably 0.1 or less.
Further, when the water soluble resin is coated only on one side, it is preferred that the water soluble resin is coated on a surface of the water-decomposable non-woven fabric to be contacted by a drying drum for drying the water-decomposable non-woven fabric in a manufacturing process thereof. Because the surface becomes relatively smooth after in contact with the drying drum, the solution of the water soluble resin, when coated, less intrudes into the non-woven fabric.
In the cleaning article of the invention, the water soluble resin is coated on a surface to be used as a cleaning surface.
The present invention also provides a method of manufacturing a cleaning article comprising:
a step of subjecting a fiber web containing water dispersible fibers to a water jetting treatment thereby forming a water-decomposable non-woven fabric,
a step of drying the water-decomposable non-woven fabric after the water jetting treatment,
a step of coating a solution of a water soluble resin with a viscosity ranging from 1,000 cps to 100,000 cps (preferably, 5,000 cps to 70,000 cps, and more preferably, 10,000 cps to 70,000 cps) on at least one side of the water-decomposable non-woven fabric after drying, and
a step of drying the coated solution of the water soluble resin.
In the method described above, it is preferred that the water-decomposable non-woven fabric after the water jetting treatment is dried by using a drying drum, and the solution of the water soluble resin is coated to the water-decomposable non-woven fabric after drying on a surface contacted by the drying drum.